My brother left his wife and two children six months ago. His wife changed all the locks and says she is going to divorce him. Although my brother has been paying the mortgage since they separated the wife says he’s lost all rights to the house. Is this correct?
No. In theory your brother could move back in (he’s entitled to force an entry if necessary), but that probably wouldn’t be a practical solution. If your sister-in-law files for divorce the court will have complete discretion as to how the property is divided, but its main concern will be the welfare of the children. It’s quite common for a wife to be allowed to remain in the house until the youngest child reaches 18, after which the property must be sold and the proceeds divided.